Motor vehicles have a plurality of electronic components or control units. To reduce the consumption of electrical power in the motor vehicle, some of these control units are transferred into a sleep mode, in case they are not in use. There are different possibilities to wake up or activate a control unit from a sleep mode when starting a motor vehicle or with an applied use. In modern motor vehicles, for example, several control units are networked via a bus line or a bus system, said bus system in a motor vehicle usually being a CAN-bus. Typically, those control units which are in a sleep mode, also known as sleep mode or stand-by mode, can be woken up or set into an operating mode by means of an activation signal, also known as wake-up signal or bus-wake-up pattern.
Such a bus system is described for example in patent specification DE 102 96 400 B4. In a communication network several control units of a motor vehicle are networked via a data bus. The network further comprises a monitoring unit, which can emit a wake-up signal onto the data bus, to wake up the individual control units as required.
Normally, therefore a sleeping control unit receives an activation signal via a bus system, whereupon an initialisation of the control unit from a sleep mode to an operating mode is effected, including the generation of internal system voltages. To reset the control unit thereafter into a sleep mode, the control unit must be able to independently receive the call to sleep from the BUS, thereupon to signal its willingness to sleep and to set itself independently into a sleep mode.
If, during the initialisation of the control unit, an error occurs, it would not be possible to deactivate the control unit again until the power supply is disconnected.
Thus, with known control units, it is disadvantageous that a defective control unit can no longer pass into a sleep mode, in particular, if there is a malfunction during initialisation of the control unit. In this case all the time power is demanded from the vehicle battery, what can lead to a failure of the power supply and thus to a breakdown of the motor vehicle.